Aminoglycoside antibiotics are essential for treating life-threatening bacterial sepsis, yet induce acute nephrotoxicity and permanent deafness/balance disorders. These noxious side-effects affect as many as 120,000 individuals each year in the US, particularly infants and premature babies. The long-term goal of this research is to prevent the cochlear uptake of aminoglycosides and subsequent ototoxicity, thus preserving life-long auditory function. Aminoglycosides like gentamicin cross the cochlear blood-labyrinth barrier into the cochlear fluids and enter sensory hair cells, inducing toxicity and hearing loss. Our recent data suggest that systemically-delivered gentamicin is trafficked from the strial vasculature, across the stria vascularis, into endolymph prior to hair-cell uptake. We have identified a candidate aminoglycoside transporter. Pharmacological inhibition of this transporter reduces cochlear, strial and hair-cell uptake of gentamicin. The specific aims of this project are: First, to determine if other aminoglycosides are predominantly trafficked to cochlear hair cells via the stria vascularis and endolymph in vivo (Aim 1). Second, to test whether inhibitors of aminoglycoside trafficking preserves auditory function by preventing hair cell toxicity, and maintain the bactericidal efficacy of aminoglycosides. We will also determine if deletion of the candidate aminoglycoside transporter ameliorates aminoglycoside ototoxicity (Aim 2). And, third, investigate whether structural modification of aminoglycosides prevents cochlear trafficking, hair cell uptake and hair cell toxicity (Aim 3). Identifying the routes and molecular mechanisms of aminoglycoside trafficking across the BLB and into hair cells is crucial to develop new pharmacotherapeutic strategies that preserve auditory function during aminoglycoside therapy. Clinically-relevant inhibitors of aminoglycoside trafficking should not affect the bactericidal efficacy of aminoglycosides. Preventing cochlear trafficking and hair cell uptake of aminoglycosides will allow clinicians to use aminoglycosides more aggressively for treating life-threatening bacterial sepsis, specific agents of bioterrorism, and for prophylaxis in combat, severe burns and blast injuries.